1. Field of the Invention
This invention relates to a method for firing a liquid propellant gun. More particularly, this invention relates to a method for firing a liquid propellant gun wherein the propellant is a solution of ammonium perchlorate in ammonia.
2. Description of the Prior Art
Liquid propellant guns offer certain advantages over conventional guns. Among these advantages are the elimination of the inconvenience and weight of cartridges. Accordingly, considerable experimentation is presently being carried out in efforts to develop liquid propellant guns.
Several experimental liquid propellant guns are now in existence. Such a gun is fired by (1) inserting a projectile into the rear of the barrel, (2) injecting liquid propellant into a chamber behind the projectile and (3) igniting the propellant. The burning propellant produces expanding gases which drive the projectile out of the barrel.
In the past, propellants for liquid propellant guns have typically been bipropellants. For example, in the early experiments a mixture of nitric acid and n-octane was used. The mixture was actually prepared in the firing or combustion chamber. That is, nitric acid was injected into the firing chamber from one source and n-octane from another source whereby the two mixed in the chamber. The mixture was then ignited and burned. The combustion produced gases which drove the projectile from the barrel.
The use of a bipropellant, i.e., a propellant composition which is mixed in the firing chamber, presents a problem in that each component must be separately removed from its source, metered and delivered to the firing chamber through its own nozzle or port. Accordingly, experimentation with monopropellants was carried out because the use of a monopropellant would permit gun simplification.
Insofar as is known by the inventors, the first monopropellant experimented with in guns was called NOS-365 and was made up of hydroxyl ammonium nitrate, isopropyl ammonium nitrate and water. Theoretical calculations with NOS-365, showed that the impetus provided by the material was low. Impetus is the driving force supplied to the projectile and may be mathematically illustrated by the formula: Impetus=nR.gamma.T.sub.o where n represents the moles of gas produced per unit mass of propellant, R is the gas constant and .gamma.T.sub.o is the isochoric flame temperature.
One of the factors which receives major consideration in selecting a propellant for use in a liquid propellant gun is the flame temperature. Since repeated charges of propellant must be put in the firing chamber in rapid succession in a multishot weapon, it is desirable to have the flame temperature as low as possible to avoid overheating the chamber. Overheating of the firing chamber may lead to many problems. Among the more obvious problems are the possibility that the chamber walls may weaken and be ruptured and the possibility that when a "shot" of propellant is injected heat may cause it to ignite immediately rather than at the desired time. Moreover, throat erosion, which produces projectile inaccuracy, is aggravated by high flame temperatures.
Since n, R and .gamma.T.sub.o are all multiplied to obtain the impetus, since R is constant and since .gamma.T.sub.o should be relatively low to avoid the above mentioned heat problems, n must be high if one is to have a propellant that produces a high impetus and yet has a low isochoric flame temperature.